Ic layout parsing for multiple masks

ABSTRACT

A method for separating features in a target layout into different mask layouts for use in a photolithographic process. Features of a target layer are searched for features having a predefined shape. In one embodiment, portions of the feature having the predefined shape divided into two or more sub-features and at least one sub-feature are not considered when separating the features into two or more mask layouts. In another embodiment, features having a predefined shape are cut to form two or more sub-features and all features and sub-features are considered when separating the features of the target layout into the two or more mask layouts.

FIELD

The disclosed technology relates to data preparation for preparing masksfor photolithographic processing, and in particular to masks to be usedin double patterning photolithographic techniques.

BACKGROUND

In conventional lithographic processing, integrated circuits are createdby exposing a pattern of features contained on a mask or reticle onto awafer that is coated with light sensitive materials. After exposure, thewafer is then chemically and mechanically processed to create thecircuit elements corresponding to the features on the wafer. The processis then repeated for the next layer of the integrated circuit in orderto build up the circuit on a layer by layer basis.

The ability of a photolithographic imaging system to accurately print adesired pattern of features on a wafer is diminished as the size and/orspacing of the features becomes smaller and smaller. Optical and otherprocess distortions occur such that the way in which small or veryclosely spaced features are printed on the wafer may vary substantiallyfrom a desired target pattern. To compensate for these distortions,numerous resolution enhancement techniques (RETs) such as optical andprocess correction (OPC), sub-resolution assist features (SRAFs), phaseshifting masks (PSMs) and others have been developed that increase thefidelity with which a target pattern of features can be printed on awafer.

One technique that can also be used to print small and/or densely packedfeatures is called double patterning. With double patterning, a targetpattern of features to be printed on a wafer is divided among two ormore masks. Each mask generally prints every other feature of the targetpattern on the wafer. The features of the second mask are positioned tobe printed in the spaces that are between the features printed by thefirst mask. Because the features on each mask are spaced farther apart,they are not distorted as much during the printing process.

Double patterning techniques are one of many multiple mask processingapproaches that assemble the final pattern using multiple exposures. Ascommonly used, the term “double exposure” refers to the use of twophotomasks to expose the same photoresist, which is then processed onlyafter all exposures are made. Some applied phase-shifting masktechniques well known in the art use double exposure, in which certainhigh resolution features are provided by one mask, while other lowerresolution features are provided by another mask. The separation oflayouts for use with double-dipole lithography, in which layouts areparsed into horizontally and vertically oriented portions for exposurewith vertical and horizontally oriented dipole illumination,respectively, is another example of a double exposure technique.

In what is commonly called “double patterning”, the layout is againparsed between two photomasks, but the process is usually designed suchthat, after the initial exposure with one mask, the wafer is processedand the patterns fixed, typically using an intermediate hard mask on thewafer. The wafer is then recoated with photoresist for exposure to thesecond photomask, followed with a second sequence of processing steps toproduce the final pattern. Since the initial layout is processed andpreserved for later use in the second patterning step, there is moreflexibility in the layout parsing rules and processing conditions underwhich double patterning can be carried out.

Despite the benefits that may be obtained with the double patterningprocess, the technique can be difficult to implement with real worldlithographic designs. In particular, it can be difficult and timeconsuming to separate a target pattern of features into two or more masklayouts in a way that ensures that each mask does not have features thatare spaced within a predetermined distance of each other. Therefore,there is a need for a more efficient technique for preparing masklayouts for use with a double patterning photolithographic process.

SUMMARY

The disclosed technology relates to a method of preparing layout datafor use with a double patterning photolithographic process. A computersystem receives data representing a target layout of features to beprinted on a wafer. The data is analyzed to identify features that haveone or more predetermined shapes. Features having one of thepredetermined shapes are broken or cut into smaller sub-features. In oneembodiment, a coloring algorithm analyzes the data representing thefeatures of the target layout in order to divide the features among twoor more mask layouts while not considering or isolating some of thesub-features. In another embodiment, a gap is introduced between thesub-features and all the features and sub-features are analyzed todivide the features of the target layout among two or more mask layouts.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a sample target layout pattern to be printed on awafer with a double patterning photolithographic process;

FIG. 2 illustrates a number of features defining a decomposition spacein accordance with one embodiment of the disclosed technology;

FIG. 3 illustrates a pair of decomposition conflicts in the targetlayout pattern shown in FIG. 2 that occur as a result of an initialseparation of the features between two mask layouts;

FIG. 4 illustrates isolated sub-features within a target layout patternin accordance with one embodiment of the disclosed technology;

FIG. 5 illustrates biasing sub-features that abut each other but aredefined for different mask layouts in accordance with another aspect ofthe disclosed technology;

FIGS. 6( a)-6(b) are flow charts of steps performed in accordance withone embodiment of the disclosed technology;

FIG. 7 illustrates how a U-shaped feature can be detected and dividedinto a number of sub-features in accordance with the one embodiment ofthe disclosed technology;

FIG. 8 illustrates how an S-shaped feature can be detected and dividedinto a number of sub-features in accordance with an embodiment of thedisclosed technology;

FIG. 9 illustrates how a T-shaped feature can be detected and dividedinto a number of sub-features in accordance with an embodiment of thedisclosed technology;

FIG. 10 illustrates another technique for detecting T-shaped features inaccordance with the disclosed technology;

FIG. 11 illustrates a sample gate layout to be created with a doublepatterning process;

FIG. 12 illustrates landing pad features from the layout shown in FIG.11;

FIG. 13 illustrates a separation of features into a first and secondmask layout;

FIG. 14 illustrates biasing narrow poly lines into the landing padfeatures in accordance with another aspect of the disclosed technology;and

FIGS. 15 and 16 illustrate the operation of a coloring algorithm toseparate features into two or more mask layouts.

DETAILED DESCRIPTION

FIG. 1 illustrates an example of a target layout pattern of features 50to be created on a wafer with a double patterning photolithographicprocess. The target layout pattern includes a number of features 52-66that are to be printed on the wafer. Typically, the features in thetarget layout pattern are defined as polygons in a layout descriptionlanguage, such as GDS-II or OASIS, and are stored in a layout database.Some of the polygons in the layout database represent circuit elementsto be created on the wafer, while others may represent non-printingfeatures such as sub-resolution assist features (SRAFs).

If the spacing between features in the target layout is sufficientlysmall, optical distortions can occur when the features are printed suchthat the shape of the features that are printed on a wafer may varysignificantly from their shape defined in the target layout pattern.

As indicated above, one approach to improving the fidelity of a printedpattern of features is to use a double patterning process, whereby thetarget pattern of features is printed with two or more masks. Each maskprints some of the features of the target pattern. However, the masksare created such that the space between each feature on a single mask islarge enough such that the features will print without significantdistortion.

FIG. 2 illustrates one technique for separating the features of a targetlayout among two or more mask layouts that is described in U.S. patentapplication Ser. No. 11/621,077, which is assigned to Mentor GraphicsCorporation of Wilsonville, Oreg., the assignee of the disclosedtechnology, and is herein incorporated by reference. In one embodimentof the disclosed technology, a decomposition space is defined bycreating new polygons that define features in selected spaces betweenfeatures of the target layout. In one embodiment, the features of thetarget layout 50 are analyzed by a computer program such as the Calibre™program suite available from Mentor Graphics to determine the distancebetween adjacent features. New polygons 70, 72, 74, 76, 78, 80, etc. aredefined in the layout database where the distances between the featuresof the target layout are less than the lithographic resolution limit ofthe lithographic process that will be used to print the features. Forexample, polygons 70 and 82 are defined between the adjacent features 52and 54 because the distance between the features 52 and 54 is less thanthe resolution limit of the photolithographic process to be used.

Once the polygons defining the features of the decomposition space havebeen created, the decomposition space can be used as an input layer to acoloring algorithm. Coloring algorithms, such as those used in PSMGatethat is part of the Calibre program suite, are often used in thecreation of phase-shifting masks to assign one property (e.g. 0 degreesof phase shift) to features on one side of a feature in the input layerand another property (e.g. 180 degrees of phase shift) to a features onanother side of the feature in the input layer. For double patterningdecomposition, the property that is assigned to the features on eachside of a feature in the input decomposition space layer is the masklayout to which the features will be assigned. For example, the coloringalgorithm may assign feature 52 that is adjacent to the polygon 82 inthe decomposition space to one mask layout and feature 54 that is on theother side of the polygon 82 to another mask layout.

For some integrated circuit layouts, it is possible to separate thefeatures of the target layout among two or more mask layouts with asingle application of a coloring algorithm. In many instances however,there is no way to assign the features of the target layout to the twoor more mask layouts in a manner that ensures that every featurecontained in a single mask layout is greater than a predetermineddistance away from an adjacent feature. FIG. 3 illustrates the targetlayout pattern shown in FIG. 2 wherein features 52, 56, 60 and 64 areassigned one value (e.g., red) by the coloring algorithm for inclusionin a first mask layout and features 54, 58 and 62 are assigned anothervalue (e.g., black) by the coloring algorithm for inclusion in a secondmask layout. However, decomposition conflicts, as indicated by 100 and102, occur where the distance between features that are assigned to thesame mask layout is less than or equal to the lithographic resolutionlimit of the photolithographic printing system. To eliminate suchconflicts, it is often desirable to break or divide larger features intotwo or more pieces (i.e., sub-features) such that one or more of thesub-features can be assigned to different mask layouts.

One aspect of the disclosed technology is a method of analyzing a targetlayout with a computer program to automatically determine those placeswhere a feature may be divided in order to facilitate the assignment offeatures to two or more mask layouts for use in a double patterningprocess.

In one embodiment of the disclosed technology, a computer programanalyzes a target layout for features having a predetermined shape suchas U-shaped, S-shaped or T-shaped features. Once features having one ofthe predefined shapes are located, the features are divided into two ormore sub-features. In one embodiment, selected sub-features are removedfrom consideration during the application of the coloring algorithm toallow the coloring algorithm to attempt to assign the remaining featuresof the target layout to the different mask layouts without decompositionconflicts.

In another embodiment, one or more gaps are added between a sub-featureand the feature from which it was divided. All the features, includingall the sub-features, can then be analyzed by the coloring algorithm toseparate the features among the two or more mask layouts.

FIG. 4 illustrates the target layout with some of the features dividedinto two or more sub-features. For example, feature 54 is shown dividedinto three sub-features: 54 a, 54 b and 54 c. Similarly, feature 60 isshown divided into three sub-features: 60 a, 60 b and 60 c. Feature 64is shown cut into four sub-features: 64 a, 64 b, 64 c and 64 d. In oneembodiment of the disclosed technology, the sub-features 54 b and 60 bare removed from consideration during the analysis of the target layoutby the coloring algorithm. The coloring algorithm is applied to theremainder of the layout and features are assigned to one of twodifferent mask layouts. In the example shown in FIG. 4, features 52, 56and 62 are assigned to a first mask layout along with sub-features 54 cand 64 a. Feature 58 and sub-features 54 a, 60 a, 60 c and 64 b, 64 cand 64 d are assigned to the second mask layout.

Comparing the assignment of features in FIG. 4 with the assignment shownin FIG. 3, it will be appreciated that the decomposition conflict 100 iseliminated because the adjacent features 56 and sub-feature 60 a areassigned to different mask layouts. Similarly sub-features 60 c and 64 aare assigned to different mask layouts to eliminate the decompositionconflict 102.

Once the mask layout assignments have been made, the sub-featurespreviously not considered from the target layout during thedecomposition analysis are added back to one of the two or more masklayouts. The sub-feature(s) not considered during application of thecoloring algorithm are added to the abutting sub-features in a mannerthat does not cause a decomposition conflict. In the example shown inFIG. 5, the sub-feature 54 b is re-connected to the sub-feature 54 a butis divided from the sub-feature 54 c, which is assigned to the secondmask layout. At the cut point between sub-features 54 b and 54 c, thepolygons that define the sub-features are extended slightly to overlapin an area 110 where they abut to compensate for any misalignment of themultiple masks that may occur during the double patterning process.Similarly, sub-feature 64 a is cut from sub-feature 64 b at an area 112.Therefore, the polygons that define these sub-features are extendedwhere the sub-features abut to compensate for any misalignment that mayoccur.

When two exposures are made using a double patterning process, eachphotomask is loaded into the lithography equipment and aligned to thewafer using registration marks. Although every effort is taken incommercial lithography equipment to make overlay errors as small aspossible, significant misalignments can still occur between the featuresprinted from the first mask and the second mask. Therefore, when finalcontiguous features must be stitched together from polygons which havebeen cut, overlay compensation should be used.

FIG. 5 has already illustrated compensation in area 110. In general,Overlay compensation is achieved by the use of selective overlaycompensation algorithms. In one embodiment of the disclosed technology,the algorithm is as follows:

1) In the case when the dimension of the portion of the feature in thefirst mask is equal to the dimension of the corresponding portion in thesecond mask, then the polygon in the first mask is extended in thedirection of the feature in the second mask by some dimension “A”, andthe polygon in the second mask is extended in the direction of thefeature in the first mask by the same amount “A”. The mutual extensionsin this case are typically in equal amounts, and form an overlap regionthat insures the final line formed will be contiguous, even in thepresence of overlay errors.

2) In the case where the dimension of the portion of the first mask is2.5 times greater than the dimension of the corresponding portion in thesecond mask, then the polygon in the first mask is not extended, whilethe polygon in the second mask is extended in the direction of thefeature in the first mask by the amount “2A”.

3) In the case where the dimension of the portion of the second mask is2.5 times greater than the dimension of the corresponding portion in thefirst mask, then the polygon in the second mask is not extended, whilethe polygon in the first mask is extended in the direction of thefeature in the first mask by the amount “2A”.

In another embodiment of the disclosed technology, features are dividedinto two or more sub-features and all sub-features are considered by thecoloring algorithm when dividing the target layout into two or more masklayouts. In one implementation, a gap is introduced in the area where afeature is divided to define a sub-feature. Polygons are added to thedecomposition space in the area of the gap. The coloring algorithmrecognizes the additional polygons that are part of the decompositionspace input layer and therefore analyzes all the features andsub-features in the layout to divide the features among the two or moremask layouts. Once the features are separated among the two or more masklayouts, the areas of the gaps are closed where two adjoiningsub-features are defined on the same mask layout. In addition, thepolygons that define the sub-features are extended in the area of thegap where adjoining sub-features are defined on different masks layouts.

FIGS. 6A-6D are flow charts of steps performed by a computer system inaccordance with one embodiment of the disclosed technology to divide alayout into multiple mask layouts for a double patterning process.Although the steps are shown and described in a particular order, itwill be appreciated that the steps may be performed in a different orderor different steps performed while still achieving the functionalitydescribed.

It should be noted that these flow charts relate to the steps taken toparse the layout data, the subject of this disclosed technology. Once alayout has been parsed into multiple mask layouts, a final step ofexporting the layouts for each of the masks must still be accomplished.These final steps are generally accomplished using standard mask datapreparation tools, designed to take internal data layers and export themin particular mask writer formats, and are therefore not the focus ofthis disclosed technology. In one embodiment, the mask layouts for theIC design are stored on a computer readable media and sent to a maskwriter that may be inside or outside of the United States.

In one embodiment of the disclosed technology, a computer system such asany electronic circuit that executes programmed instructions receivesexecutable instructions on a computer readable storage media e.g. a CD,DVD, hard disc, flash drive, etc. Alternatively, the instructions may bereceived over a wired or wireless communication link. The computersystem executes the instructions to prepare a target layout of featuredata for use with two or more masks for printing with a doublepatterning process.

Beginning at 200, the computer system receives a drawn layout or portionthereof. At 202, the computer system separates the drawn layout into atarget layer in a layout database and a remainder layer in the layoutdatabase. In one embodiment of the disclosed technology, the targetlayer comprises features having sizes that are between predetermineddimensions. Those features that are larger than, or smaller than, therange of dimensions suitable for double patterning defined in theremainder layer.

At 204, polygons that define the decomposition space layer are createdin the spaces between those features of the target layer that aresmaller than a lithographic resolution limit of the photolithographicsystem to be used. The photolithographic resolution limit may be userselected or predetermined.

At 206, a coloring algorithm is applied using the features of thedecomposition space layer as an input. In one embodiment of thedisclosed technology, the coloring algorithm used is the PSM Gatefunction provided by the Caliber software suite. However, otheralgorithms that operate to assign adjacent features in a target layer todifferent mask layouts could be used.

From the coloring algorithm, an initial separation of the features amongtwo or more mask layouts is made. For example, a first mask layout(mask_0), is defined to include one set of features from the targetlayout identified by the coloring algorithm while a second mask layout(mask_1) contains the other features of the target layout. In oneembodiment, the features assigned to each mask layout are defined inseparate layers of the layout database.

At 210, it is determined if there are any decomposition conflicts in thetwo mask layouts mask_0 and mask_1. If so, processing proceeds to thesteps shown in FIG. 6C. If not, the processing proceeds to the stepsshown in FIG. 6B.

If the initial separation of features in the target layout does notproduce any decomposition conflicts, then the features of the remainderlayer are added to one of the two mask layouts mask_0 or mask_1. At 220,the features from the remainder layer that touch the features in themask_(—)0 layout but do not touch the features in the mask_(—)1 layoutare added to the features of the mask_(—)0 layout. At 222, the featuresfrom the remainder layer that touch the features in the mask_(—)1 layoutbut do not touch the features in the mask_(—)0 layout are added to themask_(—)1 layout. At 224, the features from the remainder layer that donot touch either of the features defined in the mask_(—)0 or mask_(—)1layouts can be added to either the mask_(—)0 or mask_(—)1 layout.

Finally at 226, those features in the remainder layer that touchfeatures in both the mask_(—)0 and mask_(—)1 layouts are analyzed todetermine if the feature will be smaller than a minimum mask constraintsize if added to either of mask_(—)0 or mask_(—)1 layouts. Masks canonly be made with features that are larger than a minimum mask featuresize that is governed by a mask writing machine. If a feature is addedto a mask that is too small to be manufactured on one of the two masksthen it should be included in the other mask layout. Therefore, in oneembodiment, the features in the remainder layer that touch features inboth of the mask_(—)0 or mask_(—)1 layouts are added to that mask layoutin which the added feature size is greater than or equal to the minimumfeature size required to be manufactured on the mask. Areas of featuresthat abut but are defined in different mask layouts are extended tocompensate for any misalignment or other processing artifact that maycause a discontinuity when the abutting features are printed.

Once all the features from the remainder layer have been added to eitherof the mask layouts, processing finishes at step 230.

If the answer at step 210 indicates that there are decompositionconflicts in the mask_(—)0 or mask_(—)1 layouts produced from an initialanalysis of the target features with the coloring algorithm, thenprocessing proceeds in accordance with the steps shown in FIG. 6C.Beginning with a step 250, one embodiment of the disclosed technologysearches the target layout for features having a U, S, or T shape. Aswill be appreciated by those skilled in the art, these are not the onlyshapes that may be searched in the target layout. For example, a libraryof shapes including I-shaped, L-shaped or other shaped features may beincluded based on user experience if these shapes tend to causedecomposition conflicts.

At 254, features having a U, S, T or other shape are divided into two ormore sub-features. In one embodiment of the disclosed technology, themiddle sub-feature of a U, S shaped feature or perpendicularly orientedportion of a T-shaped feature is isolated or not considered duringapplication of the coloring algorithm as explained in further detailbelow.

At 256, the coloring algorithm is reapplied on the decomposition spacelayer without considering the isolated sub-features. The coloringalgorithm produces an initial separation of the features into themask_(—)0 and mask_(—)1 mask layouts at 258.

At 260, the computer system determines if there are one or moredecomposition conflicts in the mask_(—)0 or mask_(—)1 layouts. If so,another analysis of the target layout is performed to modify thesub-features that are isolated at 262. For example, features may bedivided into additional sub-features or the sub-features may be defineddifferently and the process of analyzing the layout with a coloringalgorithm repeats. For example, a knowledge base may be defined withfeatures that have previously been found to produce decompositionconflicts in certain situations. The target layout can be searched forfeatures having such shapes before reanalyzing the layout with thecoloring algorithm.

If there are no decomposition conflicts in the mask_(—)0 and mask_(—)1layouts, processing proceeds to the steps shown in FIG. 6D.

Once it is determined that there are no decomposition conflicts in themask_(—)0 or mask_(—)1 layouts, the features of the remainder layer areadded to the mask_(—)0 or mask_(—)1 layout at 264 in the manner definedin steps 220-226 shown in FIG. 6B.

At 266, the features in the mask_(—)0 layout that abut features definedin the mask_(—)1 layout are extended by a bias amount to overlap in thearea of the abutment. As indicated above, the bias amount ensures thatthere will be overlap in the adjoining portions of the features despitepotential misalignment or other processing artifacts during thephotolithographic printing process.

At 268, those features that are assigned to the mask_(—)1 layout andabut a feature that is defined in the mask_(—)0 layout are extended by abias amount to overlap in the area of the abutment. The process ends at270.

Upon final determination of the features that are to be assigned to themask_(—)0 and mask_(—)1 layouts, the data defined for each mask layoutcan be transmitted to a mask writer that fabricates the masks for use ina double-patterning photolithographic process.

FIG. 7 indicates one embodiment of a technique for detecting anddividing U-shaped features into two or more sub-features. In oneembodiment of the disclosed technology, U-shaped features are detectedby analyzing each feature in the target layer for features having threeconsecutive segments of length greater than zero that are joined by twoconcave 90 degree corners. The U-shaped feature 290 is divided intothree sub-features 290 a, 290 b, 290 c by defining end points for themiddle portion of the sub-feature. In one embodiment the computer usespredefined end points for each feature found that matches the desiredfeature shape. For example, the computer may define end points at theconcave corners (points 300, 302) and opposite from the corners and atthe same width as the width of the middle portion of the feature (points306, 308). Alternatively, the middle sub-feature could be defined bypoints 310, 312 and points 314, 316. As indicated above, the middlesub-feature 290 b may be ignored by the coloring algorithm whenseparating the feature into two or more mask layouts. In an alternativeembodiment, the computer system adds a gap in the feature by definingend points in the feature at one or more of the locations 320, 322 andpolygons added in the area of the gap(s) such that the coloringalgorithm can consider the sub-feature 290 b when attempting to separatethe features.

FIG. 8 illustrates one technique for finding S-shaped features in thetarget layout. An S shaped feature 330 is detected by the computer bylocating features having three consecutive segments of lengths L-1, L-2and L-3 that are greater than zero and are joined by one concave and oneconvex corner. In one embodiment of the disclosed technology, the middlesub-feature is divided from the feature by adding end points atpredetermined locations such as at the corners 332, 338 and oppositeeach of the concave and convex corners at points 336, 334 with a widthequal to the width of the middle segment. Alternatively, a gap can beintroduced by the computer between the sub-feature 330 b and itsadjoining sub-features 330 a and 330 b that is filled with a polygonthat is included in the decomposition space.

FIG. 9 illustrates one technique for detecting and dividing T-shapedfeatures 350 into two or more sub-features 350 a, 350 b. To detect aT-shaped feature 350, a search is made for a feature having a segmentwith a length L-3 that abuts another segment of length L-1 at ninetydegrees somewhere along its length as defined by distances L-2 and L-2′that are not equal to zero. The sub-feature 350 b is defined by joiningthe end points at the corners 354, 356. Either of the sub-features 350a, 350 b can be ignored during application of the coloring algorithm.Alternatively, a gap can be introduced between the sub-features 350, 352that is filled by a polygon defined for the decomposition space inputlayer.

FIG. 10 illustrates an alternative technique for detecting T-shapedfeatures. In this embodiment, the computer defines a boundary box 360the intersection of two segments. For T-shapes the boundary box includeseight vertices 362-376. In contrast, L-shapes will only contain 6vertices. By counting the vertices in the boundary box 360, the shape ofthe feature can be determined.

In the example target layout described above, the layout isrepresentative of a metal layer in an integrated circuit. The disclosedtechnology can also be used on other layers such as the gate layer. FIG.11 is an example of a portion of a gate layer that can be created with adouble patterning technique. In this example, the target layout 400 hasfeatures of a more uniform size and width that are interspersed withlarger landing pad features. In this example, the target layout includesa number of gate poly lines 402, 404, 406, 408, 410, 412, 414 and fieldpoly lines 420, 422, 424 and 426. These lines are each connected tolarger landing pad features such as landing pads 440, 442, 446 etc.

With a gate layer, one embodiment of the disclosed technology separatesfeatures the poly lines representing gates from the feature representingthe larger landing pads. Upon receipt of the target layout or portionthereof, the target layout is analyzed to find those features having awidth greater than some predefined value that identifies a feature asbeing a landing pad. Those features that are landing pads are dividedfrom the poly line features in the target layout at the junction of thelanding pads and the poly lines.

In one embodiment, the landing pad features are separated into two masklayouts mask_0 and mask_1. A decomposition space is created by definingpolygons between landing pad features that are closer than theresolution limit of the photolithographic system. Next, a coloringalgorithm separates the features into one of the two mask layouts. FIG.12 illustrates the landing pad features separated into two mask layouts.Landing pad features 440 and 446-460 are assigned to one mask layoutwhile landing pad feature 442 is assigned to the other mask layout.

The same process is applied to the poly line features in order toseparate the features into two mask layouts—mask_2 and mask_3. Next, thefour mask layouts are combined back into two mask layouts in a way thatwill not produce layouts having features that are spaced closer than theresolution limit of the lithographic system.

FIG. 13 shows how the features can be recombined. Landing pad features440, and 446-460 are assigned to one mask layout along with poly linefeatures 410, 414 and 426. The remaining poly line features and landingpad feature 442 are included on the other mask layout.

The last step for processing gate layouts is to extend those portions ofthe poly line features that abut a landing pad feature for thosepositions where the features are defined in different mask layouts. Inone embodiment, only the poly line features are biased into the areaoccupied by the landing pad feature as shown for example by areas 470,472 and 474 in FIG. 14. This has the advantage of not introducingdistortion into the landing pads by adding an extension to the features.

FIGS. 15-16 illustrate how the coloring algorithm in PSMGate assignsadjacent features in a sample layout pattern to different mask layouts.

First, each polygon that defines a feature to be parsed is assigned aunique identification number (e.g., 501, 502, 503, . . . n for npolygons—see FIG. 15). This can be only for a single cell defining oneor more feature, or for many cells in a layout. Then, each connectionbetween these polygons through features in the “decomposition space”layer is also assigned a unique identifier (e.g., g1, g2, g3, g4, . . .gm for m polygons).

These relationships are used to construct a graph, with the polygons 501through n as nodes and the features of the decomposition space layer asthe connections between the nodes. See FIG. 15. This graph is sometimescalled a conflict graph.

A node in the graph is selected as the starting point. A “Depth-FirstSearch” is then carried out, assigning the nodes to either group A orgroup B as the search progresses through the graph. A sequence of stepsfollows (as shown below), and a colored graph (indicated by plain orhashed nodes) is shown in FIG. 16.

-   -   Depth-first search coloring starting with Node 501.    -   Sequence moves generally from left to right through the layout,        following each chain encountered to its end.    -   Assign Node 501 to layer A (Hashed)    -   Node 501 connected by g1 to Node 502; assign Node 502 to layer B        (plain)    -   Node 502 connected by g2 to Node 503; assign Node 503 to layer A        (hashed)    -   Node 503 connected by g4/g6 to Node 505: assign Node 505 to        layer B (plain)    -   Node 505 connected by g5 to Node 506; assign Node 506 to layer B        (plain).        -   End of chain. Back to Node 503.    -   Node 503 connected by g3/g13/g14 to Node 504; assign Node 504 to        layer B (plain)        -   End of chain. Back to Node 503.    -   Node 503 connected by g7 to Node 507; assign Node 507 to layer B        (plain)    -   Node 507 connected by g8 to Node 508; assign Node 508 to layer A        (hashed)    -   Node 508 connected by g17 to Node 511; assign Node 511 to layer        B 510 (plain)    -   Node 511 connected by g15 to Node 510; assign Node 510 to layer        A (hashed)    -   The next step would be    -   Node 510 connected by g11/g12 to Node 503; assign Node 503 to        layer B (plain)    -   but this is not possible because Node 503 is already assigned.        Back to Node 507.    -   Node 507 connected by g9 to Node 509; assign Node 509 to layer A        (hashed)    -   The next step would he    -   Node 509 connected by g10 to Node 503; assign Node 503 to layer        B (plain)    -   but this is not possible because Node 503 is already assigned.        -   End of chain. Back to Node 511.    -   Node 511 connected to . . . (next polygon off illustrated        graph).

Once a polygon has been assigned to either group A or B, it is notreassigned. Conflicts occur when a newly assigned polygon in anotherbranch of the tree has a portion that connects to a polygon that isalready assigned. When an assigned polygon is encountered, the algorithmcurrently does nothing, and instead moves on with the next node in thesearch. Such coloring conflicts are generally referred to as “phaseconflicts” when the coloring algorithm is used to assign phase shiftvalues to polygons. However, as used herein the term coloring conflictor decomposition conflict can encompass any two polygons that areassigned to the same group and are within a predetermined distance ofeach other.

Although the polygon assignment algorithm does not identify theseconflicts as they are created, they are easily detected after theassignment is finished by using a DRC check for minimum spacing amongthe polygons assigned to collection group A or collection group B.

Note also that there need not be a single layer of features in thedecomposition space. The features can actually be on multiple datalayers as well, some assigned a higher priority than others (indicatedby the data layer used to store them). Coloring can first be done usinga graph constructed using only the high priority “features,” thenre-colored using all the features.

From the initial assignment of features into two different groups ordata layers, a determination can be made if features in each group ordata layer have the minimum separation required for printing with asingle mask. Features that are too close can be readily identified bysoftware programs which determine the distance between adjacentfeatures. If the distance is less than or equal to some predeterminedamount and the features are assigned to the same group or data layer, auser can be alerted to the fact that a decomposition conflict exists.

It should be noted that, although the examples used to illustrate thisdisclosed technology have been related to double patterning, these dataparsing techniques could be similarly used for triple patterning or, insome cases, for double or multiple exposure processes. Likewise,although these may have been illustrated with layouts which appear to bebright field (i.e. features of dark polygons on an otherwise clearbackground), these techniques could be used with either bright field ordark field layouts, as long as the separation and feature cutting rulessuitably accommodate the actual process and structures that are to beused.

Although both double patterning and double exposure require parsinglayout data, and use two photomasks and two exposures, the specificrules about separating data to the two masks can be significantlydifferent and process specific, and the process data for one approachoften cannot be exchanged for another. However, although a particulardata parsing technique may be developed for a double patterning process,it is conceivable that the same technique for data parsing could applyto some subsequent double exposure process with special characteristics,or vice versa.

In view of the many possible embodiments to which the principles of thedisclosed technology may be applied, it should be recognized that theillustrated embodiments are only preferred examples of the disclosedtechnology and should not be taken as limiting the scope of thedisclosed technology. Rather, the scope of the disclosed technology isdefined by the following claims and equivalents thereof.

1. A method of preparing layout data with a computer to create two ormore mask layouts that produce a target pattern of features with aphotolithographic process, comprising: receiving a target layout orportion thereof into a memory of the computer that defines a number offeatures to be created with the photolithographic process; searching thetarget layout received in the memory of the computer for features havinga predefined shape; isolating a portion of one or more features thathave a predefined shape; and supplying the features in the target layoutwithout the isolated portions to a coloring algorithm that assigns thefeatures of the target layout to a first mask layout or a second masklayout.
 2. The method of claim 1, further comprising: receiving a firstlayout and a second layout of features that have been assigned by thecoloring algorithm and exporting the first layout and the second layoutto a mask writing tool.
 3. The method of claim 1, further comprising:receiving into a memory of the computer system a layout pattern thatdefines a number of features to be created with the photolithographicprocess; analyzing the features in the layout pattern to determinefeatures having a size between a minimum size and a maximum size; andselecting the features of the layout pattern having a size between theminimum size and the maximum size as the features of the target layout.4. The method of claim 3, further comprising: selecting features of thelayout pattern having a size outside of the minimum or maximum size as aremainder layout.
 5. The method of claim 4, further comprising:receiving a first layout and a second layout that have been assigned bythe coloring algorithm and adding the features of the remainder layoutto either of the first layout or the second layout.
 6. The method ofclaim 5, further comprising: determining if the addition of features inthe remainder layout would violate a mask constraint and adding thefeatures to either of the first layout or the second layout such thatthe addition does not violate a mask constraint.
 7. The method of claim1, wherein the target layout is searched for features having a U-shape.8. The method of claim 1, wherein the target layout is searched forfeatures having an S-shape.
 9. The method of claim 1, wherein the targetlayout is searched for features having a T-shape.
 10. The method ofclaim 7, further comprising: isolating a middle portion of a U-shapedfeature by adding a cut point at a predefined position in the U-shapedfeature.
 11. The method of claim 8, further comprising: isolating amiddle portion of an S-shaped feature by adding a cut point at apredefined position of the S-shaped feature.
 12. The method of claim 9,further comprising: isolating a portion of a T-shaped feature by addinga cut point at a predefined position of the T-shaped feature.
 13. Themethod of claim 1, further comprising adding the isolated portions ofthe features to the features in the first mask or the second masklayouts.
 14. The method of claim 13, further comprising: determiningwhere features in the first and second mask abut in the target layoutand extending at least one of the abutting features to overlap the otherin the area of the abutment.
 15. The method of claim 13, furthercomprising: determining if the abutting features are substantially thesame size, and if so, extending both abutting features to overlap theother in the area of the abutment.
 16. The method of claim 13, furthercomprising: determining if one of the abutting features is larger thanthe other abutting feature, and if so, extending a smaller abuttingfeature to extend into an area of a larger abutting feature.
 17. Acomputer storage medium including a number of instructions that areexecutable by a computer to perform any of method claims 1-16.
 18. Acomputer storage medium including a first mask layout and a second masklayout that are used to produce a pattern of features on a wafer with aphotolithographic process that is produced by any of claims 1-16.
 19. Amethod of preparing layout data with a computer to create two or moremask layouts that produce a target pattern of features with aphotolithographic process, comprising: receiving a target layout orportion thereof into a memory of the computer that defines a number offeatures to be created with the photolithographic process; searching thetarget layout received for features having a predefined shape;introducing at least one cut point at a predefined location of featuresthat have the predefined shape to create separate sub-features; andproviding the features and sub-features to a coloring algorithm thatdivides the features and the sub-features of the target layout betweenthe two or more mask layouts such that no feature on the mask layouts isspaced less than a predetermined distance from an adjacent feature ofthe mask layout.
 20. The method of claim 19, wherein the features andsub-features are provided to a coloring algorithm by defining additionalfeatures that are between features in the target layout having aseparation of less than a predetermined amount and between the cutpoints; and supplying the additional features as an input to a coloringalgorithm that assigns features on opposite sides of the additionalfeatures to different mask layouts.
 21. The method of claim 19, whereinthe predefined shape is a U-shape.
 22. The method of claim 19, whereinthe predefined shape is an S-shape.
 23. The method of claim 19, whereinthe predefined shape is a T-shape.
 24. The method of claim 19, furthercomprising: determining where features defined on different mask layoutsabut in the target layout and extending at least one of the abuttingfeatures into an area of the abutting feature.
 25. The method of claim24, further comprising: determining if the abutting features aresubstantially the same size, and if so, extending both abutting featuresto overlap the other in the area of the abutment.
 26. The method ofclaim 24, further comprising: determining if one of the abuttingfeatures is larger than the other abutting feature, and if so, extendinga smaller abutting feature to extend into an area of a larger abuttingfeature.
 27. A computer readable storage medium including a number ofinstructions that are executable by a computer to perform any of themethod claims 19-26.
 28. A computer readable storage medium including afirst mask layout and a second mask layout that are used to produce apattern of features on a wafer with a multiple exposurephotolithographic process produced by any of method claims 19-26.
 29. Acomputer system that executes a sequence of instructions to perform anyof the method claims 1-15.
 30. A computer system that executes asequence of instructions to perform any of the method claims 19-26.